Mixed cellulose ethers



United States Patent 3,357,971 MIXED CELLULOSE ETHERS Eugene D. Klug, Wilmington, Del., assignor to Hercules Incorporated, a corporation of Delaware No Drawing. Filed July 6, 1964, Ser. No. 380,686 14 Claims. (Cl. 260-215) The present invention relates to mixed cellulose derivatives, and more particularly to hydroxypropyl cellulose containing an ionic substituent and having unexpected beneficial properties. Considered another way, the present invention relates to a hydroxypropyl cellulose having unexpected beneficial properties by virtue, in part at least, of ionic substituent groups having been introduced to a limited degree of substitution (D.S.).

My copending application Serial No. 257,064, now Patent No. 3,278,521, filed on February 8, 1963, and entitled, Hydroxypropyl Cellulose and Process, discloses and claims a novel hydroxypropyl cellulose. Surprisingly, the hydroxypropyl cellulose of said copending application is characterized by the following desirable properties:

(1) Soluble in cold water.-

(2) Insoluble in hot water.

(3) Thermoplastic.

(4) Soluble in a large number of polar organic solvents.

(5) Low equilibrium moisture content.

In solubility in hot water is a distinct and important advantage in that it permits purification with hot water to a low ash content as compared with purification with aqueous organic liquids which not only have the disadvantage of being far more expensive but they complicate the process because they must be recovered. Furthermore, even with large amounts of organic solvents, an ash content as low as with hot water cannot be obtained. However, this hot water insolubility of the hydroxypropyl cellulose product restricts its use, because in certain applications the hydroxypropyl cellulose must remain in solution at elevated temperatures.

An object of the present invention is to modify the hydroxypropyl cellulose product disclosed and claimed in my above-identified copending application in such a way to substantially increase the temperature at which it remains soluble in water and at the same time maintain the above-mentioned other desirable properties of said hydroxypropyl cellulose. A further object is to provide a mixed cellulose derivative containing hydroxypropyl substituent and ionic substituent characterized by having the unexpected and desired properties of the hydroxypropyl cellulose disclosed and claimed in my above-identified copending application and at the same time being soluble in hot water at a substantially higher temperature than said hydroxypropyl cellulose.

The above and other objects are accomplished in ac-' cordance with the present invention by making a mixed. water-soluble cellulose derivative by carrying out the process which comprises reacting cellulosic material with a hydroxypropylating agent and a second agent which imparts ionic character to said cellulose derivative until the product has an ionic D8. of 0.001 -0.4 and a hydroxypropyl M.S. of at least 2, and recovering the mixed cellulose derivative. v

For the sake of brevity the following designations will be used sometimes hereinafter: CM is carboxymethyl, HP is hydroxypropyl, MCA is monochloroacetic acid, DEAE is diethylaminoethyl, and TBA is tertiary butyl alcohol.

The purpose of the following paragraph is to explain the use herein and in the prior art of the terms degree 70 of substitution (D.S.) and M.Sf

There are three hydroxyl groups in each anhydrow glucose unit in the cellulose molecule. BS. is the average number of hydroxyl groups substituted in the cellulose .per anhydroglucose unit. M.S. is the average number of moles of reactant combined with the cellulose per anhydroglucose unit. For the alkyl, sulfoalkyl, sulfate, dialkylaminoalkyl, carboxyalkyl, or acyl derivatives of cellulose, the D.S. and M.S. are the same. For the hydroxyalkyl derivatives of cellulose, the M.S. is generally greater than the D8. The reason for this is that each time a hydroxyalkyl group is introduced into the cellulose molecule, an additional hydroxyl group is formed which itself is capable of hydroxyalkylation. As a result of this, side chains of considerable length may form on the cellulose molecule. The M.S./D.S. ratio represents the average length of these side chains. Thus, from the foregoing it will be seen that the D8. of a cellulose derivative can be no higher than 3, whereas the MS. may be considerably higher than 3, depending on the extent to which side chains are formed.

The substitution values of the modified hydroxypropyl cellulose derivatives of the present invention were analyzed as follows. The derivatives containing carboxyl groups were purified in the free acid form and the carboxyl substitutions were determined by titration to the phenolphthalein end point of the base. The sulfonic acid and'sulfate substitutions were determined by analysis for sulfur content. The dialkylaminoalkyl substitutions were determined by analysis for nitrogen content. The following examples illustrate various embodiments of the present invention but they are not intended to limit the invention beyond the scope of the appended claims. In these examples and elsewhere herein, unless otherwise indicated, percent and parts are by weight and all viscosities were determined with a standard Brookfield Synchro-Lectric LVF viscometer using an aqueous solution of the cellulose derivatives of the concentration specified and at a temperature of 25 C. The cellulose derivatives of the present invention may be prepared by introducing into cellulose the hydroxypropyl substituent and the ionic substituent in any order desired, but it is preferred to introduce the hydroxypropyl and ionic substituents in the same step or to introduce the ionic substituent and then the hydroxypropyl substituent.

In these examples a measure of the hot water solubility of the mixed cellulose derivatives was obtained from the opaque temperature. The value for the opaque temperature was obtained by raising the temperature of a 1% or 2% aqueous solution of the product at a rate of 15 C.- 2 C. per minute. This was done in a test tube in which a thermometer was immersed. The lowest temperature atwhich the solution became opaque was recorded as the opaque temperature.

Sodium hydroxide was used to adjust the pH of the aqueous solutions of the mixed cellulose derivatives, except the diethylaminoethyl hydroxypropyl cellulose was adjusted with acetic acid.

The following Examples 1-5 illustrate the preparation of the mixed cellulose derivatives of the present invention by hydroxypropylating low substituted ionic cellulose derivatives. The carboxymethyl cellulose was prepared in accordance with Klug and Tinsley US. Patent No. 2.517.577.

EXAMPLES 1-52-STEP REACTION Example 1.-Carboxyrnethyl hydroxypropyl cellulose One part of finely divided carboxymethyl cellulose (having a D8. of 0.18 and thus being insoluble in water) was slurried in 2.35 parts TBA, 8.6 parts hexane and 0.1 part water. 0.2 part of 50% aqueous NaOH was added to the slurry. The slurry was stirred for an additional hour at room temperature, after which it was transferred to a a 4 pressure vessel to which 3.0 parts. propylene oxide was TABLE-3 added. The pressure vessel was sealed and the mixture was l r reaction] heated at 70 C. for 16 hours. Agitation was employed throughout the. process. 2% Aqueous 80mm At the end of the reaction, part of the alkali Wasneuii p Ionic DS HP tralized by adding 0.1 part acetic acid. Most of the hexane MS ig pH @39 2? was removed. by decanting and the remaininghexane was distilled off by contacting the product with live steam. v

The carboxymethyl hydroxypropyl cellulose product 1 a .18 M 4.2 9.5 gt; was added in small amounts to vigorously stirred water 5 97 at 85 C.95 C.,-the pH being maintained at 3.0 by incre- 3-8 mentally adding H PO of 85% concentration. After all 2 OM OM 25 40 of the carboxymethyl hydroxypropyl cellulose had been 3 0 48 CM 4 5 34 g5 added, the resulting slurry was stirredfor an additional 78 minutes and tnen the pH adjusted to 3.0. Upon discon- 15 $3 tinuingv the agitation of the slurry, the carboxymethyl 4 0.1 a51)E.-4E 3.7 12.5 311 73 hydroxpropyl cellulose product settled out quickly and p Z 51 the water was removed by decanting. The purification of 5 0M7 thev carhoxymethyl hydroxypropyl cellulose product was a 1 a completed by subjecting it to three additional steps com- Examples l-5 hereinbefore illustrate preparing mixed prising slurrying in hot Water, allowing to settle and de- Cellulose derivatives of the present invention by a 2-step canting, while maintaining the pH at about 3.0. The final reaction, i.e. by. introducing into cellulose an ionic subpurified carboxymethyl hydroxypropyl cellulose product stituent to a low D.S. and then hydroxypropylating said was roll dried at about 120 C. ionic cellulosederivative. Another method of preparing the mixed cellulose derivatives of the present invention Examples 2 x hydwxypmpyl comprises introducing the ionic and the hydroxyp'ropyl celluose substituents in a l-step reaction, i.e. inthe same operation. These two experiments were carried out using the same following x mples 6-22 illustrate the l-steP di i i Example 1, except that carboxymethyi tion. These examples also show the introduction of various cellulose of diiterent D.S. values was used in order to other ionic substituents. obtain carboxymethyl hydroxypropyl cellulose of different EXAMPLES 6-111-STEP REACTION carboxymethyl values- Example 6.'Carb0xymetlzyl hydroxypropyl cellulose Example 4;Diethylamin0ethyl lzyclroxypropyl cellulose One part finely divided wood pulp was slurried'in 6.6 This experiment was carried out using the same condit t fe l 9 1 Partwatel? A Sohmon of 0049a tions as in Example 1, except that diethylaminoethyl cellu- MC d S N m Parts T w addd to the l lose was hydroxypropyl'ated and except that the diethyl- Slurry r l p' paflpf ,NaOH w adfkd to aminoethyl hydroxypropyl cellulose product was purified the E? and h wi e one The Slur W w at pH 7. The diethylaminoethyl cellulose in this example a l d F P d. and parts propylene and elsewhere herein was prepared in accordance with 40 oxlfle j q l h 5 g." a 6 b l at 70 Vaughan US Patent No. 2,623,042. Agitation was employed throughout the process. These carboxymethyl hydroxypro'p'yl cellulose products were Example 5 .--Carb0xy-l hydroxypropy-l cellulose purified and dried under the same conditions of Examples This experiment was carried out using. the same. condif j i fl p Tame. 2 heremaftet tions as in Example 1,,except that carboxyl-cellulose was Examples 1 y y py 6611141058 hydroxypropylated. T hecarboxylcellulose was. prepared in These examples were carried out under the same condiaccordance with Kenyon and Yackel US. Patent No. tions as Example-,6 except the amount of MCA was varied 2,448,892. in order to obtain carboxymethyl hydroxypropyl cellulose Further details of Examples l-5 appear in Table 1 5O productshavirigdififerent-carboxymethyl D.S. values. Fur hereinafter. therdetails appear in Table 2'hereiuafter.

TABLE 2 [l-Step reaction) Weight .Ratios to Air-Dry Aqueous Solutions Cellulose 1 Example HP OM N0, M DS mm, Viscosity; Opaque H2O NaOH MCA percent 0p. pH Temperature, C.2

0; 0.30 r 0.124 0. 025 4.21 0204' 2 3715 314 43' I 5.1 50 7.0 52 7 0.31 0.135 0. 04 4. 2 0. 07' 2 41" 2:9 43 5.0 50 7.1 64 a. 0. 30 0.180 0.00 3.5- 0.16 1 240 3.0 45- 5.0 75 7.0 81 9 0. 40 0.105 0.11 4.2 0.18 2 25 2.85 44 4. 05 71 v 5.05 97 10 0. 40 0. 238. 0.15 4.4 0. 2e 2 1,100 3.2 4.0 3.4 6.5 5.0 97 7.0 07 11 0. 40 0. 274 0. 20 4.1 0. 30 2 450 3. 2 4g 1 The propylene oxide/cellulose ratio was 3.0. in Examples 6-11. p 1 Theopaque temperature of unmodifiedhydroxypropyl cellulose 1s approximately 40 0-45" 0.

The following Examples 1222 illustrate preparation of mixed cellulose derivatives of the present invention by the l-step reaction employing several other reagents which impart ionic character to the derivatives. In Examples 12-16, carboxyethyl ionic substituent was introduced to varying D5. and various reagents were used for this purpose.

The following was the procedure employed in these Examples 12-22. To a slurry of one part cellulose, 8.6 parts hexane and 2.35 parts t-butanol, a variable amount of water and ionic reagent was stirred at room temperature. To the resulting slurry was added 50% NaOH aqueous slurry in an amount such that 0.1 part of 100% NaOH would be present in the reaction mixture in excess of the amount consumed during the reaction. The water/cellulose ratio, including the water in the 50% NaOH, amounted to approximately 0.4. After the slurry was stirred one hour at room temperature, 3 parts propylene oxide was added. The reaction mixture was heated with agitation for 16 hours at 70 C.

The mixed cellulose derivatives prepared in accordance with'these Examples 1222 were purified as set forth in Example 1 hereinbefore, except that the diethylaminoethyl hydroxypropyl cellulose product was purified at pH 7.

Further details of Examples 1222 appear in Table 3 hereinafter,

The log of flow was plotted in inches per two minutes against l/T i.e. against the reciprocal of the absolute temperature, giving a straight line. From this line was read off the temperature at which the product flowed one inch in two minutes at 500 p.s.i. Further details appear in Table 4 hereinafter.

TABLE 4 [Plastic iiow] Product of Example HP MS CM DS Tinius-Olsen Flow No. Temp., 0. at 500 p.s.i.

TABLE 3 [1-Step reaction] 2% Aqueous Solution Example Ionic Cellulose Derivative Ionic Reagent, g./g. cellulose Ionic 1 N o. Visc., pH Opaque D.S.'

cp. Temp, 0 C.

B-Chloropropionic acid 0.025 7.1 73 0.03 li-Chloropropionic' acid, 0.05 7. 1 98 0. 05 Acrylonitrile, 7.0 98 0. 04 Acrylamide, 0.05. 7. 05 98 0. 08 .do Methyl acrylat 7. 05 92 0. 05 a-Methyl carboxymethyl cellulose a-Chloropi'opionic acid, 190 7. 05 86 0.07 Sultoethyl cellulose Sodium vinyl sulfonate, 0.13 670 7.0 59 0.03 do Sodium fl-chloroethyl sulionate, 0.05-. 2, 000 7. 1 08 0. 008 Sultopropyl cellulose Propanesultone 0.06 320 7. 0 71 0. 013 Sulfate cellulose Triethylamine-sulinr trioxide complex, 0.10. 20 7. O 64 0. 017 Dimethyi aminoethyl cellulos Diethylaminoethyl-chloride hydrochloride, 0.10 408 3.05 98 0.028

1 All products had HP MS values of 3.5-4.5.

Both diethylaminoethyl hydroxypropyl cellulose and dimethylaminoisopropyl hydroxypropyl cellulose of substantially the same substitution values as the dimethyl aminoethyl hydroxypropyl cellulose of Example 22 in Table 3 hereinbefore were prepared using the conditions of Example 22, except employing different aminoalkylation reagents. These latter two mixed celloluse derivatives also possess the same desirable properties including substantially increased opaque temperature, of the Example 22 product.-

The modified hydroxypropyl cellulose derivatives of the present invention retain most of the thermoplasticity of the unmodified hydroxypropyl cellulose defined herein. Thermoplasticity of the carboxymethyl hydroxypropyl cellulose products of Examples 7 and 9 hereinbefore was determined as follows under the application of heat and pressure in an Olsen Bakelite flow tester. This is a standard testing device widely used in the plastics industry. It is described in ASTM method D569-46A (ASTM Standards, 1958, Part 9, page 393). This device is perhaps more often referred to in the art as the Tinius-Olsen flow tester. The carboxymethyl hydroxypropyl cellulose was ground toa fine powder and conditioned over CaCl and therefore was substantially bone dry when tested. Cylindrical pellets /8" x were formed from this powder in a pelleting machine. The pellet was placed in the Tinius- Olsen flow tester and the plastic flow thereof measured.

2, preferably 3-10, 4 being specifically preferred. Hydroxypropyl cellulose having an ionic D.S. value even as low as 0.001 has an opaque temperature noticeably higher than said hydroxypropyl cellulose without the ionic substituent. Increasing the ionic D8. of said hydroxypropyl cellulose increases the opaque temperature. In some cases'an ionic D8. of only 0.04 increased the opaque temperature to substantially the boiling point of water (i.e. to about C.). An ionic D.S. range of 0.001-04 is operable in accordance with the present invention but a range of 0.01-0.12 is preferred.

The particular manner of introducing the ionic substituent is not per se a part of the present invention; in fact, it is not critical and any conventional process is applicable. Various methods are known in the prior art for accomplishing this.

An important and unexpected aspect of the present invention is that reacting cellulosic material with a hydroxypropylating agent and an ionic agent to a low ionic D.S. gives a mixed cellulose derivative which is soluble in water to a substantially higher temperature than unmodified hydroxypropyl cellulose when these ionic substituent groups are in the salt form. When the ionic substituent groups are present mainly in the nonsalt form, then the mixed cellulose derivative is substantially insoluble in hot water and may be purified with hot water during its preparation. In practice this means that during preparation the pH of the mixed derivative is adjusted to a low level of about 2-3 for those containing certain ionic substituents including carboxylic acid, sulfonic acid, phosphate and sulfate, etc. substituents. On the other hand, the amine type mixed cellulose derivatives including dialkylaminoalkyl hydroxypropyl cellulose are best purified at a pH of about 7 because at low pH this type forms acids salts which are water-soluble at elevated temperatures. The pH may be decreased by employing any suitable acid and the pH may be raised by employing compounds which will supply ions of alkali metals. For instance, hydrochloric acid, phosphoric acid, acetic acid, sodium bicarbonate, sodium hydroxide and potassium hydroxide are quite suitable for adjusting the pH to the desired value.

Another important and unexpected property is the variation of the aqueous viscosity of these products with temperature. This may be studied by means of the Brabender Viscograph which records the viscosity continuously as the temperature is raised from C. to 97 C. at the rate of 1.5 C per minute. With unmodified hydroxypropyl cellulose there is a normal decrease in viscosity as the temperature increases followed by an abrupt disappearance of viscosity at C. C., the temperature at which precipitation occurs. With the modified hydroxypropyl celluloses of this invention, the viscosity behavior at pH levels where the product remains soluble varies depending on the ionic substitution, pH, solution concentration, molecular weight of the product, and rate of shear. In some cases, the decrease in viscosity with temperature is similar to that of a watersoluble polymer which exhibits no insolubility in hot Water. In other cases, the viscosity does not drop as rapidly. In some instances, the viscosity temperature curve goes through a minimum and over a certain temperature range the viscosity increases with temperature. In extreme cases, the viscosity at some elevated temperature may be many times the viscosity at room temperature. An interesting and unusual property of aqueous solutions of the mixed cellulose derivatives of the present invention is that as the temperature is lowered, the curves are generally reversible. This frequently is not the case with solutions of other water-soluble polymers which gel on heating.

The presence of very small amounts of an ionic substituent has a surprisingly large effect on the solubility in hot water and consequently on the solution viscosity. This effect is greatest when the ionic substituent is in its most highly ionized state and the effect is very slight or nonexistent when the substituent is relatively un-ionized. Consequently, this behavior is strongly influenced by pH. The effect of pH on the different classes of substituents is as follows.

Carboxylic acids-These include carboxyl cellulose and carboxyalkyl cellulose. Carboxylic acids are comparatively Weak and at low pH levels are very slightly ionized but at pH levels above 5, where they are in the salt form, they are highly ionized. These derivatives are therefore quite soluble in hot water at pH levels above 5 but are insoluble in hot water at pH levels of 3 or less. They may be purified in hot Water at the low pH levels. Solubility of these products in water at 40 C. or less is of course good regardless of pH.

Dialkylaminoalkyl hydroxypropyl cellulose derivatives.-At neutral or higher pH levels these derivatives are substantially nonionic and are insoluble in hot water. They do become ionic at low pH levels as shown by the following equation:

purified in hot Water at a pH of about 7.

SlllfOItiC acid and sulfates.-These are stronger acids and therefore their solubility is less sensitive to variations in pH. They are best purified at very low pH values.

Although not necessary, purification of the products of the present invention is facilitated by washing with dilute aqueous salt solution, e.g. 1% sodium chloride, instead of water alone. This has a fiocculating and/or salting out effect on the products and facilitates handling. Purification with aqueous salt solutions is especially beneficial with products containing the higher amounts of ionic substituent.

From the foregoing temperature-viscosity disclosure regarding the products of this invention it will be apparent that by proper control of conditions it is possible to thicken compositions when the temperature is raised. The utility of this desirable property will be illustrated hereinafter.

It has been mentioned hereinbefore (pages 2 and 16) that While unmodified hydroxYPIOPB/l Cellulose as described and claimed in my copending application identifled on page 2 hereof has many desirable properties, it is not applicable where realizing the benefits of these properties depends on the unmodified hydroxypropyl celluloze being in aqueous solution at temperatures above about 40 C.45 C. because it precipitates out of solution above this temperature (herein and in said copending application referred to as its opaque temperature). These uses includes, e.g., those in which it is desired to use the hydroxypropyl cellulose as a thickener, a stabilizer or surfactant at elevated temperature such as, e.g., in paints, adhesives and foods. By modifying said hydroxypropyl cellulose in accordance with the present invention the opaque temperature is raised so thatthe modified hydroxypropyl cellulose is applicable in fields of the type enumerated.

As many apparent and widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiment thereof except as defined in the appended claims.

What I claim and desire to protect by Letters Patent 1. Process of preparing a mixed cellulose derivative comprising mixing cellulosic material, alkali, water and a water miscible inert organic diluent, and then causing the alkali cellulose to react with hydroxypropylating agent and a second agent which imparts ionic character to the cellulose derivative, continuing the reaction until said derivative has a hydroxypropyl MS. and an ionic D8. of at least 2 and (1001-04, respectively the alkali/ cellulose ratio being (102-05, the water/cellulose ratio being 0.1.4 and O.12 in the alkali cellulose period and etherification gperio-d, respectively.

2. Process of claim 1 wherein said second agent is an etherifying agent.

3. Process of claim 2 wherein said etherifying agent is carboxyalkylating agent.

4. Process of claim 2 wherein said etherifying agent is dialkylaminoallrylating agent.

5. Process of claim 2 wherein said etherifying agent is sulfoalltylating agent.

6. Process of claim 1 wherein said second agent is an esterifying agent.

'7. Process of claim 6 wherein said esterifyin g agent is sulfating agent.

8. As a new compound hydroxypropyl cellulose containing ionic substituent having a hydroxyp ropyl MS. of at least 2 and an ionic MS. of 0.0( )10.4, which is thermoplastic, soluble in cold water and polar organic solvents, said new compound also being soluble in hot water to a substantially higher temperature than unmodified hydroxypropyl cellulose which has an MS. of at least 2 and is thermoplastic, soluble in cold Water and polar organic solvents.

9. Compound of claim 8 wherein is ether substituent.

the ionic substituent 16 10. Compound of claim 9 wherein the ether substituent References Cited is carboxyalkyl ether substituent. UNITED STATES PATENTS 1 1. Compound of clann 9 wherein the ether substltuent 2618632 11/1952 Klug v 260-231 1s dralkylarmnoalkyl substltuent.

12 C d f 9 h th the b flu 5 2,591,748 4/1952 Vaughan 260231 c W mm 6 e r S 1 2,132,181 10/1938 Neu-gebauer 2150-931 XR ent is sulfoalkyl substituent.

13. Compound of claim 8 wherein .the ionic substituent DONALD CZAJA, Primary Examiner is ester substituent.

14. Compound of claim 13 wherein the ester substituent LEON BERCOVITZ Examine is sulfate substituent. 10 R. W. MULCAHY, Assistant Examiner. 

1. PROCESS OF PREPARING A MIXED CELLULOSE DERIVATIVE COMPRISING MIXING CELLULOSIC MATERIAL, ALKALI, WATER AND A WATER MISCIBLE INERT ORGANIC DILUENT, AND THEN CAUSING THE ALKALI CELLULOSE TO REACT WITH HYDROXYPROPYLATING AGENT AND A SECOND AGENT WHICH IMPARTS IONIC CHARACTER TO THE CELLULOSE DERIVATIVE, CONTAINUING THE REACTION UNTIL SAID DERIVATIVE HAS A HYDROXYPROPYL M.S. AND AN IONIC D.S. OF AT LEAST 2 AND 0.00U-0.4, RESPECTIVELY THE ALKALI/ CELLULOSE RATIO BEING 0.02-0.5, THE WATER/CELLULOSE RATIO BEING 0.1-4 AND 0.1-2 IN THE ALKALI CELLULOSE PERIOD AND ETHERIFICATION PERIOD, RESPECTIVELY. 